1. Technical Field
The present invention relates to a media conveyance control method that can suppress variation in the tension on the medium when conveying a continuous medium delivered and conveyed from a roll, and to a printer.
2. Related Art
A printer that prints on continuous recording paper delivered from a paper roll according to the related art is described in JP-A-H08-133540, for example. The printer described in JP-A-H08-133540 has a conveyance mechanism that conveys recording paper through a conveyance path past a print position, and a media supply motor for rotating the paper roll. JP-A-H08-133540 also describes forming a loop in the recording paper between the conveyance mechanism and the paper roll, and having a loop sensor that detects whether or not the loop is appropriately formed. When conveyance of the recording paper starts, the media supply motor is driven to rotate the paper roll so that the loop is desirably formed, and thereby reduces the load on the conveyance mechanism.
If the tension on the recording paper varies due to change in the diameter of the paper roll, for example, slipping may occur between the conveyance mechanism and the recording paper, and the conveyance speed of the recording paper may change. Because variation in the conveyance speed can lead to a drop in print quality, suppressing variation in the tension on the recording paper while the recording paper is being conveyed in the printer is desirable.
To suppress variation in the tension on the recording paper while the recording paper is being conveyed, a movable member that can move following variation in the tension on the recording paper between the paper roll and the conveyance mechanism may be provided, and delivery and take-up of the recording paper from the paper roll may conceivably be controlled to keep the movable member positioned at a target position set in the range of movement of the movable member. This can be achieved by, for example, regularly determining the deviation in the position of the movable member from the target position while conveying the recording paper, and using feedback control of the media supply motor to rotate the paper roll to minimize the acquired deviation as it is detected.
When such a configuration is used, however, the power supply to the media supply motor increases when a no-paper error or other error occurs while conveying the recording paper, possibly causing the media supply motor to overheat. For example, when printing with recording paper that has the trailing end glued to the core of the paper roll, and the end of the recording paper is reached, the recording paper will be pulled by the conveyance mechanism in the conveyance direction D while the trailing end of the paper is pulled in the opposite direction as the conveyance direction D by the core of the paper roll, and the recording paper will become locked and not conveyed. When this happens, the movable member remains stuck at the end of its range of movement on the side where the tension on the recording paper increases, and the media supply motor is therefore driven to rotate the paper roll in the direction delivering the recording paper in order to return the movable member to the target position. Because the deviation in the position of the movable member does not decrease in this event, even more power is supplied to the media supply motor as time passes, and the media supply motor may overheat.
When printing with recording paper that does not have the trailing end glued to the core of the paper roll and the recording paper ends, the recording paper will unravel from the core near the trailing end of the paper, and the force pulling the recording paper in the opposite direction as the conveyance direction D will disappear. In this event, the movable member becomes stuck at the end of its range of movement on the side where the tension on the recording paper is low, and the media supply motor is driven to rotate the paper roll in the direction that takes up the recording paper in order to return the movable member to the target position. Because the deviation in the position of the movable member does not decrease in this event, even more power is supplied to the media supply motor as time passes, and the media supply motor may overheat.
Furthermore, if the recording paper jams while the recording paper is being conveyed and the portion of the recording paper that jammed pushes the movable member to the end of its range of movement, the deviation in the position of the movable member does not decrease, even more power is supplied to the media supply motor as time passes, and the media supply motor may overheat. The recording paper will also continue being delivered from the paper roll in this event because driving the media supply motor continues.
Driving the media supply motor under conditions that can lead to overheating can conceivably be avoided by providing the printer with dedicated sensors for detecting conveyance errors when the recording paper ends or a paper jam occurs, for example. However, providing such sensors increases the manufacturing cost accordingly.